I guess it may be easier to take a taxi straight there from the airport, otherwise you have to change a few stations using MRT. Not sure if there is any direct bus from airport to Wong Tai Sin Temple.

If you are tourist and likes to enjoy sightseeing, you can always catch a bus which uses Cross Harbour Tunnel at Hung Hum then transfer to another bus upon reaching Kowloon to go to the temple. During busy hours, for the fastest trip, you should take MTR to go direct from Aberdeen to save the trouble of sitting in traffic jam along the way. Just ask around. It shouldn't be a problem as Wong Tai Sin is famous enough in HK. Enjoy...

No it’s free admission. If you want to burn incense there is a small charge to buy them.

Like approx 2 hours

free

don't know the buses, the MTR is so simple on the Kowloon line, Dont recall the exact stop/